1. Field of the Invention
The present invention relates to a sleepiness level detection device for detecting the sleepiness level of a test subject who operates equipment such as a vehicle and the like.
2. Description of the Related Art
Conventionally, as disclosed in Japanese Patent Laid-Open Publication No. Sho 60-15240 (1985), a device calculates the heart rate of the driver of a vehicle on the basis of, for example, the electric potential difference between electrodes provided in a steering wheel of the vehicle, in order to judge a state of tension or dozing of the driver on the basis of the heart rate. To be more specific, the device detects R-waves, having a high pulse-height value, and the like of heart potential, and converts time intervals of occurrence of the R-waves into the driver's heart rate in a heart rate conversion circuit. The heart rate decreases during sleep, and increases during tension, which is experienced during an awake state. Thus, the heart rate converted by the heart rate conversion circuit is compared with a predetermined heart rate range to judge whether the heart rate is abnormally higher or lower than the predetermined heart rate. When the heart rate is not in the predetermined heart rate range, the device issues a warning with an alarm lamp, a buzzer, or the like, and also tightens a seat belt to give a physical warning to the driver.
As described above, the conventional device determines whether the driver is in a normal physical state or in a state of tension or dozing, simply on the basis of whether or not the heart rate is in the predetermined heart rate range. As to the dozing state of the driver of the vehicle, however, the driver does not suddenly fall asleep from a conscious state, but the driver eventually reaches the dozing state after gradual increase in a sleepiness level. In the case of driving the vehicle or other equipment, the driver has less attention and the like even in a state of increasing the sleepiness level, as compared with his/her conscious state. Thus, it is desirable that the state of increasing sleepiness be precisely detected. This is because if the sleepiness level of the driver of a vehicle or an operator of equipment is precisely detected, it is possible to take appropriate measures such as issuing a warning in accordance with the sleepiness level, or restricting the operation of the equipment, and the like.